1. Field of the Invention
The present invention relates to a rectangular battery, especially rectangular battery comprising a group of electrode plates having a positive electrode plate and a negative electrode plate laminated on each other with a separator provided interposed therebetween such as nickel-hydrogen storage battery and nickel-cadmium storage battery.
2. Description of the Related Art
In recent years, a rectangular alkaline storage battery has been developed to enhance the volumetric efficiency of the interior of the apparatus using battery as a substitute for cylindrical alkaline storage battery comprising a coiled group of electrodes formed by spirally winding a positive electrode plate and a negative electrode plate with a separator provided interposed therebetween. This type of a rectangular alkaline storage battery is prepared by a process which comprises inserting into a rectangular can a group of electrode plates having a positive electrode plate and a negative electrode plate alternately laminated on each other with a separator provided interposed therebetween, connecting a positive electrode lead extending from the positive electrode plate and a negative electrode lead extending from the negative electrode plate to the positive electrode terminal and the negative electrode terminal, respectively, injecting an electrolytic solution into the can, and then sealing the can at the opening portion with a sealing material.
This type of a rectangular alkaline storage battery has found rapidly growing demand as a power supply for portable apparatus such as portable telephone and notebook type personal computer. As a result, the rectangular alkaline storage battery has been required to have a higher capacity and a prolonged life. To this end, this type of a rectangular alkaline storage battery is prepared, e.g., by a process which comprises forming a pair of horizontally arranged negative electrode plates having a belt-like core material in common with each other, bending the central portion (connection portion) of the pair of negative electrode plates into a U-shape, sandwiching a positive electrode plate by the two negative electrode plates connected to each other through a U-shaped bent with a separator provided interposed therebetween to form an electrode plate unit, laminating a positive electrode plate between the electrode plate units with a separator provided interposed therebetween to form a group of electrode plates, and then inserting the group of electrode plates into a rectangular can with an electrolytic solution.
When the thickness of the separator, which doesn""t take part in the charge-discharge reaction of the battery, is reduced to further enhance the energy density of the foregoing rectangular alkaline storage battery, the packed amount of the active material can be increased by the amount corresponding to the reduction in the thickness of the separator, making it possible to obtain a high energy density and capacity battery.
However, the smaller the thickness of the separator is for higher energy density and capacity, the lower is the mechanical strength of the separator and the more likely is internal short-circuiting. Thus, the reduction of the thickness of the separator is limited.
When a rectangular alkaline storage battery is prepared by sandwiching a positive electrode plate 10D by a pair of negative electrode plates 24, 25 connected to each other through a central U-shaped bent portion (connecting portion) 23 with a separator 30 provided interposed therebetween to form an electrode plate unit, laminating a positive electrode plate 10D between a pair of the electrode plate units with a separator 30 provided interposed therebetween to form a group of electrode plates, and then inserting the group of electrode plates into a rectangular can with an electrolytic solution as shown in FIG. 7, six sheets of the separator 30 are required.
When the number of sheets of separators disposed inside the battery is reduced instead of reducing the thickness of the separator to increase the thickness of the electrode plate by the amount corresponding to the reduction of the thickness of the separator and hence increase the packed amount of the active material, e.g., when a rectangular alkaline storage battery is prepared by a process which comprises sandwiching a positive electrode plate 10E having a great thickness by a pair of negative electrode plates 26, 27 connected to each other through a central U-shaped bent portion (connecting portion) 23 to form an electrode plate unit, laminating two such electrode plate units to form a group of electrode plates, and then inserting the group of electrode plates into a rectangular can with an electrolytic solution as shown in FIG. 8, only four sheets of the separator are required.
Thus, when the number of sheets of separators disposed inside the battery is reduced instead of reducing the thickness of the separator, the thickness of the electrode plate can be increased by the amount corresponding to the reduction of the number of sheets of separators, making it possible to increase the packed amount of the active material. Thus, a high energy density and capacity battery can be obtained.
However, the foregoing approach is disadvantageous in that it is difficult to prepare an electrode plate having a great thickness by packing an active material at a high density. The foregoing approach is also disadvantageous in that when an electrode plate comprising as a core material a three-dimensionally network porous substrate (e.g., expanded (forming) nickel) is prepared, it is difficult to increase the thickness of the electrode plate itself.
In the light of the foregoing disadvantages, the present invention has been worked out to provide a rectangular battery such as a rectangular alkaline storage battery comprising an electrode plate which can be easily prepared and having a high packing density of active material and volumetric energy density.
In order to solve the foregoing problems, the rectangular alkaline storage battery of the invention comprises as an electrode plate unit a group of electrode plates having a pair of one electrode plates (e.g., negative electrode plate) and a composite electrode plate made of a plurality of the other electrode plates (e.g., positive electrode plate) sandwiched by the pair of one electrode plates with a separator provided interposed therebetween. There is provided one such an electrode plate unit or a laminate of a plurality of such electrode plate units. In this arrangement of group of electrode plates, there is no need to dispose a separator between the electrode plate units, making it possible to reduce the number of sheets of separators to be disposed in the group of electrode plates.
By reducing the number of sheets of separators to be disposed in the group of electrode plates, the thickness of one electrode plate and the other electrode plate can be increased by the amount corresponding to the reduction in the number of sheets of separators. By increasing the number of sheets of electrode plates instead of increasing the thickness of the electrode plates, the thickness per sheet of electrode plate can be reduced. As a result, the active material can be packed at a high density. At the same time, a three-dimensional network porous substrate (e.g., expanded nickel) can be used as an electrode core material. Accordingly, the volumetric energy density of the electrode plate can be enhanced, making it possible to obtain a high capacity rectangular alkaline storage battery.
Further, when at least one collector lead plate is fixed to the composite electrode plate extending therefrom, and the collector lead plate is disposed in such an arrangement that it doesn""t come in contact with the separator at the fixing point thereof, short-circuiting due to piercing through separator by burr developed during the formation of collector lead plate can be prevented. Moreover, when such a collector lead plate is provided on the various electrode plates constituting the composite electrode plate in such an arrangement that the collector lead plates face each other at the welded portion thereof so that the electrode plate comes in contact with the separator, short-circuiting due to piercing through separator can be prevented.
Further, when one collector lead plate is fixed between the various electrode plates constituting the composite electrode plate, and an arrangement is made such that electricity is collected from the various electrode plates through the collector lead plate, short-circuiting due to piercing through separator can be prevented because the collector lead plate is disposed in such an arrangement that it doesn""t come in contact with the separator at the fixing point thereof. At the same time, the number of collector lead plates can be reduced.
Further, the pair of one electrode plates are connected to each other through a connecting portion made of the core material of these electrode plates and integrally formed therewith. When the connecting portion is bent in almost U-shaped form, a composite electrode plate can be merely disposed between the pair of one electrode plates connected to each other through the U-shaped bent connecting portion with a separator provided interposed therebetween to form an electrode plate unit easily. Thus, this type of a group of electrode plates can be easily formed.
A first aspect of the battery is a rectangular battery comprising a positive electrode, a negative electrode and a separator interposed therebetween, wherein at least one of the positive electrode and the negative electrode has a composite electrode plate made of a plurality of the other electrode plates.
A second aspect of the battery is a rectangular battery which comprises a group of electrode plates having one electrode plate and the other electrode plate laminated on each other with a separator provided interposed therebetween, wherein said group of electrodes comprises a laminate of a plurality of electrode plate units each having a composite electrode plate made of a plurality of the other electrode plates sandwiched by a pair of said one electrode plates with said separator provided interposed therebetween.
A third aspect of the battery is a rectangular battery according to the first aspect, wherein said rectangular battery is a rectangular alkaline storage battery.
A fourth aspect of the battery is a rectangular battery according to the first aspect, wherein at least one collector lead plate is bonded to said composite electrode plate extending therefrom and said collector lead plate is disposed in such an arrangement that it doesn""t come in contact with said separator at the bonded portion thereof.
A fifth aspect of the battery is a rectangular battery according to the first aspect, wherein a collector lead plate is fixed between the electrode plates constituting said composite electrode plate and electric charge is collected from the electrode plates constituting said composite electrode plate through said collector lead plate.
A sixth aspect of the battery is a rectangular battery according to the first aspect, wherein the composite electrode plate is constituted by bonding the juxtaposed electrode plates through the collector lead plate sandwiched between one ends of the electrode plates and the bonded surfaces of the electrode plates are electrode plate core surfaces exposed of active material, and electrode plates are bonded by bonding the electrode plate core surfaces to the collector lead plate.
A seventh aspect of the battery is a rectangular battery according to the first aspect, wherein said one electrode plates are connected to each other through a connecting portion made of the core constituting said electrode plates and integrally formed with said electrode plates and said connecting portion is bent in almost U-shaped form so that said composite electrode plate is sandwiched by said one electrode plates connected to each other through said almost U-shaped connecting portion.
An eighth aspect of the battery is a rectangular battery according to the first aspect, wherein at least anyone of said electrode plates comprises a core material comprising a metal porous material and an active material packed in said electrode plate.
A ninth aspect of the battery is a rectangular battery according to the sixth aspect, wherein the core material is made of expanded nickel, having a three-dimensionally continuous space was packed with the active material slurry comprising nickel hydroxide as a main component.
A tenth aspect of the battery is a rectangular battery according to the first aspect, wherein said composite electrode plate constitutes a positive electrode.
An eleventh aspect of the battery is a rectangular battery according to the first aspect, wherein said one electrode plate is made of a core metal coated with an active material paste.
A twelfth aspect of the battery is a rectangular battery according to the seventh aspect, wherein said one electrode plate is made of a core metal of punching metal, both side surfaces of which are coated with an active material paste except for said U-shaped connecting portion.
A thirteenth aspect of the battery is a rectangular battery according to the seventh aspect, wherein said one electrode plate is made of a core metal made of metal mesh, both side surfaces of which are coated with an active material paste except for said U-shaped connecting portion.
A fourteenth aspect of the battery is a rectangular battery according to the seventh aspect, wherein a plurality of the groups of electrode plates are laminated in closed-end prismatic rectangular metal can in such an arrangement that the one electrode at the both ends of the groups of electrode, the inner surface of the metal can came in close contact with each other, said U-shaped connecting portion is in close contact with the inner bottom surface of the metal can, the composite electrode is connected with at lease one of the collector lead, and the metal can is filled with an electrolytic solution.
A fifteenth aspect of the battery is a rectangular battery according to the second aspect, wherein said one electrode plate is made of a composite electrode plate.